How does my brain remember useless facts but forget important things?

I can remember random scenes from years ago. lyrics of songs i don't even like.
but important task?
gone.
how does this make sense?

Because the brain remembers what is emotionally charged and attention-grabbing, not what is "important."

A nonsensical memory contains a strong emotion or is frequently repeated.
Important information, on the other hand, is usually emotionless and one-off.
Unfortunately, I experience this situation too.